One problem with a hatchback can be that the sloping rear promotes adhesion and eddy formation (see Kamm tail).
You sometimes see big wings stuck on the back in an attempt to fix this. Here is a Toyota Soupra like the one I used to own:
The problem is that the wing actually harmed the aerodynamics.
I was able to verify this by crossing the state of Nevada in this car and then later in a Honda Prelude. I did it in 3 hours in the Quaalude and it was very stable at speed. The Supra was not at all stable even tho I drove slower. I loved that nice inline 6 cylinder tho. The Honda was fun when you revved the little 4.
Toyota started calling the wing a "sunshade"...